Mechanism for anticipating the concentration of sand in a dredging suspension

ABSTRACT

In underwater dredging, the ambient pressure in the soil or sand being dredged adjacent the tip of the dredging pipe which is buried in the sand is used to control the dredging machinery so that the output of dredged material is increased. A pressure sensitive device is used to anticipate variations in concentration of the sand in the suspension of sand in water being dredged.

ite ties atent Inventors Jan De Honing Amsterdam; Romhe Van der Veen,Jutplmas, both of, Netherlands Appl. No. 729,229

Filed May 15,1968

Patented June 29, 1971 Assignee N. V. ingenieurshureau voor Systemen enOctrouien Spnnstanl Rotterdam, Netherlands May 24, 1967 NetherlandsPriority MECHANISM FOR ANTICIPATING THE CONCENTRATKON 0F SAND IN ADREDGING SUSPENSION 2 Claims, 4 Drawing Figs.

Int. C1 E02f 3/88 Field of Search 37/58, 59,

DIG. 19; 73/299301; 302/35, 42

m1 sesame [56] References Cited UNITED STATES PATENTS 934,031 9/1909Askew 37/58 2,661,550 12/1953 Graham 1. 37/58 1,255,034 1/1918Mason,.... 73/301 2,328,954 9/1943 Conley 1 1 4 1 1 73/301 2,645,1287/1953 Walker et a1. 73/300 X 2,931,225 4/1960 Pleuger 73130] X3,224,121 12/1965 Denning 37/58 FOREIGN PATENTS 999,635 7/1965 GreatBritain 302/42 6,501,404 8/1966 Netherlands 37/58 6,501,405 8/1966Netherlands 37/58 Primary Examiner-William B. Penn AssistantExaminer-C1ifiord D. Crowder Attorney-Snyder and Butrum ABSTRACT: Inunderwater dredging, the ambient pressure in the soil or sand beingdredged adjacent the tip of the dredging pipe which is buried in thesand is used to control the dredging machinery so that the output ofdredged material is increased. A pressure sensitive device is used toanticipate variations in concentration of the sand in the suspension ofsand in water being dredged.

PATENTEU JUN29 |97i INVENTOR 3 JAN 0E KaNinc RONKE VAN DER VEENATTORNIc'YS MECHANISM FOR ANTICIPATING TIIE CONCENTRATION OF SAND IN ADREDGING SUSPENSION The invention relates to a suction dredgerinstallation, comprising a suction pipe connected to a pump. A knownsuction dredger installation of the kind specified is used in many casesfor sucking up dredger spoil, the end of the suction pipe being insertedin the soil. The suction process is then influenced by the particularvarying circumstances present adjacent the end of the suction pipe. Theoutput which can be obtained with the prior art suction dredgerinstallation depends considerably on the technical skill and experienceof the dredging supervisor in groping in the dark.

The invention provides an improved suction dredger installation which ischaracterized by at least one pressure-sensitive element which sensesthe pressure, in the soil adjacent the end of the suction pipe.

A larger output can be obtained with the improved suction dredgerinstallation according to the invention if the pressure in the soiladjacent the end of the suction pipe is known. This is an importantindication which is not available with the prior art suction'dredgerinstallation. Hitherto, for regulating the suction process, a quantityto be regulated e.g., the conveyed concentration of dredger spoil in thesuspension sucked up, has been regulated by measuring this quantity, ora quantity dependent thereon, in the suction pipe and correcting thisquantity in dependence on the difference between the measurcd andrequired values, whereas the suction dredger installation accordingtothe invention enables the future value of the quantity to be regulatedto be predicted by taking into account the pressure in the soil adjacentthe end of the suction pipe, thus also enabling this particular quantityto be regulated in anticipation, in dependence on the pressure in thesoil.

in a further development of the suction dredger installation accordingto the invention at least one regulating member for regulating thesuction process is acted upon by the sensed value emanating from thefirst-mentioned pressure-sensitive element.

Preferably, the pressure-sensing element forms part of a depth-measuringsystem for measuring the depth at which the end of the suction pipe issituated below the surface of the soil.

if it is known at what depth the end of the suction pipe is situated inthe dredger spoil the suction pipe can be duly displaced, or dulyinserted more deeply into the soil, to prevent clay and other impuritiesfloating on the sand from being sucked up instead of sand. When the toplayer of the soil is being sucked up there is a considerable risk thatthe suction mouth may be clogged by large objects which are otten to befound on the surface of the soil. Stagnation caused by clogging of thiskind can be substantially obviated by using the suction dredgerinstallation according to the invention.

Preferably, the suction dredger installation according to the inventionis so constructed that the depth-measuring system comprises apressure-difference pickup, one side of which is acted upon by thefirst-mentioned pressure-sensing element disposed adjacent the end ofthe suction pipe, the other side being acted upon by a secondpressure-sensitive element which senses the water pressure above thesoil.

These and other features of the invention will be clearly gathered fromthe following description of a number of cmbcdimsnts of a suctiondredger installation according to the invention, with reference to thediagrammatic drawings. wherein: 3

FlG. i is s drawing illustrating a suction dredger installationaccording to thc invention during the sucking up of sand and FIG. 2, 3and 4 each show the lower end of the suction pipe of variant embodimentsof the suction dredger installation according to the invention.

The suction dredger installation according to the invention shown inFIG. 1 comprises a ship 10, a pump ii, a pressure line 12 connected tothe pressure side of the pump ii, and s suction pipe 13 which has asuction mouth 20 and is connected to the suction side of the pump 11. inthe embodiment illustrated, the pump 11 is disposed at. the level of thewater 14, and the suction pipe 13 can pivot around the center line ofthe pump 11.

P10. 1 shows (counting upwards) a layer of sand 15, a layer of clay 16,and water 18. The free end of the suction pipe 13 is inserted into thesoil, to a great depth, for instance 20 m. The soil shown enclosed by achaindot line 19 and surrounding the end of the suction pipe 13 isbrought into suspension by underdigging. Outside the line 19, the :soilis in its normal undisturbed condition.

if during the sucking up of sand, the quantity of sand brought intosuspension which is still above the suction mouth 20 is known, thisquantity can be taken into account during the sucking up of sand and thedisplacement of the suction pipe 13.

To this end, the suction dredger installation shown in FIG. 1 has ameasuring system mainly consisting of a pressure pickup 21 at the end ofthe suction pipe 13 and an indicator 22. The pressure pickup 21measures, by means of a pressure-sensitive element forming part of thepressure pickup 21 and not shown in detail, the local prevailingpressure produced by a column of sand H a column of clay li and a columnof water H,.

The indicator 22 consists of a pointer 23 which is attached to thesuction pipe 13 and has a graduated scale 24 from which the angle a canbe read off, which the suction pipe 13 encloses with the horizontalplane.

The depth H of the pressure pickup 21 below the surface 14 of the wateris equal to k sin a, where k :is the length of the suction pipe from thesurface 14 of the water to the pressure pickup 21. The height H of thecolumn of sand can now be calculated by the equation:

Where:

P is the pressure measured by the pressure pickup 2i,

l! is the water column 8,, is the specific weight of the clay H, is thecolumn of clay and S, is the specific weight of the sand.

From the two above equations there follows:

The column of clay l-i,, and the specific weight 5,, are measured bycarrying out drillings. The specific weight 8,, of the drifting sand isa value known for a particular kind of sand, for instance, l.8 kgJdm".

The column of sand H can be measured considerably more simply andaccurately by means of a known pressure-difference pickup 25 which isused in the suction pipe 45 illustrated in FIG. 2; in thepressure-difference pickup 25 one pressure chamber 28 is acted upon bythe local pressure in the soil the other pressure chamber 26 beingconnected via a line 27 to the water 18 above the soil. in this case therelative pressure pickup 25 measures a pressure The pressure chamber 28is separated from the soil by a diaphragm 17. Thus the measuringdiaphragm 47 is protected from damage. The diaphragm 17 forms a firstpressure-sensing element which is directly acted upon by the pressure inthe soil and transmits this pressure via the liquid in the chamber 28 tothe measuring diaphragm 47, while the inlet aperture 46 of the line 2.7forms the second pressure-sensing element, from which the sensedpressure is transmitted via the liquid in the line 27 and in the chamber26 to the measuring diaphragm 47.

The suction pipe 323 shown in F116. 3 has a measuring system formed by apressure water line 29 which is connected to a pressure source andbranches into two narrow branches 3t 31 which have respectively a firstoutflow aperture 32 in the soil adjacent the suction mouth 34, thusforming a first pressuresensing element, and an outflow aperture 33which discharges above the soil into the water 18, thus forming a secondpressure-sensitive element, Adjacent the outflow apertures 32, 33 thebranches 3th, 311 are connected to either side of the pressure-difference pickup 3'7 via measuring lines 35 and 36 respectively.The pressuredifference pickup 37 thus measures the difference inpressure between the apertures 32 and 33. The column of sand H above theoutflow aperture 3?. can be derived therefrom.

, The suction pipe 325 shown in FIG. 3 comprises a pipe 39 which isconnected to the pump ill, and a telescopic pipe 40 which can be movedaxially in the pipe 39 by a hydraulic ram 41. Disposed around the pipe39 and the telescopic pipe 30, is an external jacket 42 which isattached to the pipe 39 and whose upper side is open and incommunication with the water 13. The suction mouth 3% in which a heavysuspension of a large quantity of sand with a little water enters, isdisposed at the lower end of the outer jacket 42. In proportion as thetelescopic pipe 30 is drawn further upwards, a larger quantity of watercomes into the telescopic pipe 4 via the outer jacket 42 along the loweredge 43 of the telescopic pipe db, and is also sucked up. On the otherhand, the sand rises higher in the outer jacket M3 in proportion as thejacket 42 is inserted more deeply into the soil. The concentration ofsand in 'the suckedup suspension can now be regulated by adjusting thedistance of the edge 43 above the suction mouth 34 in depen' dence onthe depth thereof in the soil, or in other words in dependence on thepressure measured by the relative pressure pickup 37.

The measuring system is very useful for regulating the concentration ofdredge: spoil in the suckedup suspension.

The aperture 32, and the pressure pickups 2H and 25 are preferably notdisposed in exactly the same place as the suction mouth, but at a smalldistance m thereabove, where the flows around the suction mouth havelittle effect on the pressure measured, if any. when determining thedepth of the suction mouth, the depth of the pressure pickup is thenadded with m sin a.

The pressure pickup 21 and the relative pressure pickups 25 and 37 are,for instance, of the known electric type and are each connected viaelectric wires to an indicating system (not shown) disposed on thecontrol panel on board of the ship.

The members of the suction pipe 138 shown in FIG. 4 corresponding withmembers of the suction pipe 38, have like reference numbers that are MWhigher however.

The suction pipe 138 has a measuring system formed by a pressure waterline 129 which is connected to a water source and has an outflowaperture 132 in the soil adjacent the suction mouth 13 1, the outflowaperture 132 forming a pressuresensitive element connected via ameasuring line 135 to a pressure pickup 137 whose diaphragm 144 picks upthe pressure sensed in the soil. The electric output signal from thepressure pickup 137 is fed via a line 148 to a measuring member 149which operates a hydraulic regulating valve 150. This regulating valve150 controls a hydraulic ram 141 for adjusting the height of telescopicpipe 140.

The output signal from the pressure pickup 137 can also be controlled byother regulating members (not shown) for regulating the suction process,for instance, the governor (not shown) of the pump motor. Moreover, aswell as being adjusted in dependence on the pressure in the soil sensedby the pressure-sensitive element, the height of the telescopic pipe M0in relation to the suction mouth 134 can be adjusted in dependence onother measured values (not indicated in detail).

What we claim is:

)1. A suction dredger assembly of the type including a fluid pump havinga suction inlet and a pressure outlet, and

dredging conduit means havingone end connected to said suction inlet andhaving an opposite end inserted below the bottom of a body of water intoa region of material desired to be dredged so as to deliver a suspensionof said material in water at said outlet of the pump, the improvement ofwhich comprises,

pressure sensing means supported on said opposite end of the conduitmeans for producing an output signal proportional to the pressure insaid material outside said opposite end of the conduit means whereby thedepth at which said opposite end of the conduit means is situated insaid material may be determined; and

control means for controlling said dredger assembly to maximize theoutput of said material delivered by said pump in accordance with thepressure sensed by said pressure sensing means.

2. The assembly as defined in claim 1, wherein said conduit meanscomprises an outer pipe defining, at its lower extremity, said oppositeend of the conduit means, and having its upper extremity above the levelof said bottom and within said body of water, an inner pipe connected atits upper end to said suction inlet and having a lower end portionpresenting a lower extremity disposed within the confines of said outerpipe;

said control means being connected to said lower end portion of saidinner pipe for varying the spacing between the lower extremity of saidinner pipe with respect to the lower extremity of said outer pipe.

1. A suction dredger assembly of the type including a fluid pump havinga suction inlet and a pressure outlet, and dredging conduit means havingone end connected to said suction inlet and having an opposite endinserted below the bottom of a body of water into a region of materialdesired to be dredged so as to deliver a suspension of said material inwater at said outlet of the pump, the improvement of which comprises,pressure sensing means supported on said opposite end of the conduitmeans for producing an output signal proportional to the pressure insaid material outside said opposite end of the conduit means whereby thedepth at which said opposite end of the conduit means is situated insaid material may be determined; and control means for controlling saiddredger assembly to maximize the output of said material delivered bysaid pump in accordance with the pressure sensed by said pressuresensing means.
 2. The assembly as defined in claim 1, wherein saidconduit means comprises an outer pipe defining, at its lower extremity,said opposite end of the conduit means, and having its upper extremityabove the level of said bottom and within said body of water, an innerpipe connected at its upper end to said suction inlet and having a lowerend portion presenting a lower extremity disposed within the confines ofsaid outer pipe; said control means being connected to said lower endportion of said inner pipe for varying the spacing between the lowerextremity of said inner pipe with respect to the lower extremity of saidouter pipe.